The present invention relates to a rotational angle detector and a rotational angle detecting method that are used for detecting a rotational angle of a steering wheel of a car.
Recently, functions of cars have been improved, and thus more cars have detected rotational angles of the steering wheels using various rotational angle detectors to perform various controls. Such a conventional rotational angle detector is described with reference to FIG. 8 and FIG. 9.
FIG. 8 is a perspective view of an essential part of the conventional rotational angle detector, and FIG. 9 is a voltage waveform chart. A central part of disk-like rotary body 1 has engaging part 1A engaging with an inserted steering shaft (not shown), and the outer periphery of it has a plurality of transparent holes 1B with a predetermined pitch. Photo-interrupters 2, 3 having vertically facing light emitting element and light receiving element are disposed so as to sandwich transparent holes 1B in rotary body 1. Photo-interrupters 2, 3 are held by holding member 4 at predetermined positions slightly deviated from transparent holes 1B so that detection signals having a predetermined phase difference are obtained from the rotation of rotary body 1. Wiring board 5 has a plurality of wiring patterns (not shown) on its both faces and has an electronic circuit (not shown) formed of a microcomputer or the like. The electronic circuit is connected to photo-interrupters 2, 3 and generates detection signal 6.
When a steering wheel is rotated in the structure discussed above, rotary body 1 is rotated and transmission of light through transparent holes 1B and cut-off of light are repeated. Detection signals 6, 7 having respective continuous cyclic square waveforms having the phase difference as shown in FIG. 9 are supplied from photo-interrupters 2, 3 to an electronic circuit. Here, photo-interrupter 2 outputs detection signal 6, and photo-interrupter 3 outputs detection signal 7.
A rotational angle of rotary body 1 is detected by counting the number of the waveforms of one of detection signals 6, 7. A rotational direction of rotary body 1 is detected based on the phase difference between respective waveforms of detection signals 6, 7. For example, when the waveform of detection signal 6 comes after the waveform of detection signal 7 the rotation is determined to be clockwise, and when the waveform of detection signal 6 comes before the waveform of detection signal 7 the rotation is determined counterclockwise.
In this structure, resolution is calculated as described below. When the pitch of transparent holes 1B of rotary body 1 is set at 6 degrees, widths of the holes are set at 3 degrees, and the phase difference between respective waveforms supplied from photo-interrupters 2, 3 is set to be xc2xc cycle, for example, respective waveforms of detection signals 6, 7 have cycle of 6 degrees and are shifted in phase by xc2xc cycle. Therefore, the rotational angle detector can detect a rotational angle with accuracy up to {fraction (6/4)}=1.5 degrees. In other words, the rotational angle detector has a resolution of 1.5 degrees.
Such a rotational angle detector detects a rotational angle using two sets of photo-interrupters 2, 3 and rotary body 1 having a plurality of transparent holes 1B. These components are complexly arranged and machined to increase the cost, decrease of the pitch and width of transparent holes 1B is limited, and therefore the angle detection with high resolution is difficult.
A rotational angle detector of the present invention detects, with a detecting unit, rotation of a rotary body as a detection signal having a continuous cyclic waveform that gradually increases or decreases in one cycle. The rotational angle detector is structured so that a controller calculates the detection signal as a rotational angle of the rotary body. A rotational angle detecting method of the present invention comprises the steps of:
A) detecting the rotation of the rotary body rotating in cooperation with a steering wheel as a detection signal having a continuous cyclic waveform: and
B) calculating the detection signal as a rotational angle of the rotary body.
The detection signal comprises a waveform gradually increasing or a gradually decreasing in one cycle.